Soft, poured substrates of gypsum-based materials, which may be disposed over gypsum boards or other boards, or which may be formed wood fiber-filled, inorganic, hydraulic cement are used widely in roofing installations. Materials for such substrates formed of gypsum-based materials, and used over gypsum boards or other boards, are available commercially from various sources. Materials for such substrates formed of wood fiber-filled, inorganic, hydraulic cement are available commercially from Tectum, Inc., of Newark, Ohio, under its TECTUM.TM. trademark.
In fastening blankets of roofing insulation, such as, for example, rigid slabs of fibrous insulation or of foamed insulation, to such substrates, possibly with other roofing materials therebetween, fastening assemblies of a type disclosed in Blucher et al. U.S. Pat. Nos. 4,642,012 and 4,856,951 are widely used. Such fastening assemblies are available commercially from ITW Buildex (a division of Illinois Tool Works Inc.) of Itasca, Ill., under its GYPTEC.TM. trademark.
Typically, as disclosed within each of the aforementioned patents, such a fastening assembly utilizes four separate pieces, namely an elongate screw having threads at one end of its shank and having a head, an anchoring element attached to the threaded end of the screw shank, a washer between the screw head and the anchoring element, and a plate. The plate may also be called a roofing washer. The threaded end of the shank of the screw is threaded into an axial bore of the anchoring element. The anchoring element has external threads designed to be highly resistant to pull-out from a soft substrate. The plate is disposed between the washer and a rigid slab of roofing insulation when the screw is threadedly engaged so as to drive the anchoring element.
Giannuzzi U.S. Pat. Nos. 4,763,456 and 4,892,429 contain similar disclosures of a fastening assembly employing a screw having a generally uniform crest diameter and a progressively tapered root diameter, along with a roofing washer. Bidwell U.S. Pat. No. 74,489 discloses a similar screw having a generally uniform crest diameter and a progressively tapered root diameter.
Although fastening assemblies of the type disclosed in the Blucher et al. patents noted above are satisfactory in many applications, there has been a need, to which this invention is addressed, for an improved fastener useful where such fastening assemblies are employed.